This invention relates to a rotary washing apparatus for aircrafts, and more particularly it is concerned with a rotary washing apparatus which is equipped with a control device for preventing the scrubber from being pressed against a surface portion to be washed of the airframe of an aircraft with an excessively great force.
Heretofore, it has been usual practice to rely on manual operations performed by operators to wash by scrubbing the external skin surface of an aircraft. Proposals have, however, been made to mechanically perform this washing operation as disclosed, for example, in co-pending applications U.S. Ser. No. 722,972 filed on Apr. 12, 1985 and U.S. Ser. No. 770,922 filed on Aug. 30, 1985, of which some of the applicants are the same as those among the applicants of the present application. In the systems described in these copending applications, an aircraft is placed on a turntable installed on the ground level, and a plurality of washing machines each having a rotary washing apparatus are moved to positions close to an aircraft to perform washing operations.
An aircraft is complex in construction and shape and different types of aircraft have different sizes. An aircraft is usually of monocoque construction which has a thin outer shell or skin and a framework for supporting the skin. The external surface of the skin is low in contact surface pressure strength, and this strength is, for example, about 0.35 kgf/cm.sup.2 at a single skin portion formed of aluminum alloy and about 0.1 kgf/cm.sup.2 at a honeycomb structure portion. For this reason, rotary scrubbers, such as rotary brushes, have been widely in use for washing an aircraft. In the aircraft washing apparatus designed to perform washing operations mechanically, it is necessary to control the force with which the rotary scrubbers are pressed against the external skin surface of an aircraft both for achieving excellent washing results and for avoiding damage to the skin.
Control devices suitable for use with an aircraft washing apparatus may include a device of the direct contact type using limit switches or other known means and a device of the distance measuring system which utilizes magnetism, ultrasonic waves or light rays. The control device of the former type would, however, experience difficulty in effecting adjustments of proper contact and abnormal contact in amount owing to the construction of switches and other parts. In the device of the latter type, magnetism does not act on nonmetallic skin portion formed as of fiber reinforced plastic material, and the condition of reflection of ultrasonic waves and light rays may vary depending on the curvature of the external skin surface of the aircraft. This would make it difficult to make correct measurements and make the control device complex in construction.
Japanese Patent Unexamined Publication Nos. 126294/1983 and 126295/1983 propose to use a washing apparatus equipped with pressing means for rendering uniform the pressure at which a rotary scrubber or brush presses against the external skin surface of an aircraft to wash the same by scrubbing. In this washing apparatus, the rotary brush is supported by arms pivotally mounted on a movable part of a main body of the washing apparatus. The brush pressing means imparts a rotary torque to the arms so as to force the brush against a surface portion to be washed of the air-craft, and at the same time monitors the angle of elevation of the arms. When the angle of elevation of the arms deviates from a predetermined range of angles for such a reason as a change in the contour of the surface portion to be washed, the movable part of the main body of the apparatus is moved vertically to adjust the distance between the external skin surface that is being washed and the brush so as to render uniform the pressure at which the brush rubs against the external skin surface. Like the direct contact system referred to hereinabove, this control system would suffer the disadvantage that difficulty is experienced in adjusting the range of pivotal movements of the brush supporting arms in such a manner that the pivotal movement of the arms matches the adequate amount of contact of the rotary brush with the outer skin surface. Moreover, since adjustments of the pressure at which the rotary brush presses against the external skin surface are effected by moving the movable part of the main body of the washing apparatus, the control device would become complex in construction and yet it might be impossible to promptly cope with a abrupt change in the pressure at which the brush presses against the external skin surface to be washed. In other words, the apparatus disclosed in Japanese Unexamined Patent Publication Nos. 126294/83 and 126295/83 would be able to achieve satisfactory washing results when the surface to be washed is planar. In the case of aircraft, however, the external skin surfaces are curved and include surface portions which cannot be secured in place. Aircraft wings have surface portions that cannot be secured in place, for example. Owing to their structures of cantilever, the wings have a characteristic such that a wind tends to cause them to move upwardly and downwardly when the aircraft is stationary on the ground. In the case of aircraft B-747 (trade name) generally referred to as a jumbo jetliner, its wings have been ascertained to move vertically .+-.20 cm when exposed to the wind of a velocity of 12 m/sec. No consideration is given to this specific characteristic of the aircraft structure in the prior art documents referred to hereinabove. Thus the problem with regard to the safety of aircraft would be encountered in the rotary washing apparatus of the prior art.